The present invention generally relates to laser processing systems for providing the drilling of holes in printed circuit boards, and relates in particular to such laser processing systems that provide improved speed and accuracy in the processing of printed circuit boards. The holes may used to provide paths (or vias) through the circuit boards.
It is known that laser drilling of holes is often done using a laser beam positioned with an optical scanner, such as for example, a galvanometric optical scanner. A galvanometric optical scanner generally includes a scan mirror coupled to a limited rotation motor. Such scanners are commonly referred to as “galvos” or “galvo scanners”, and examples of such scanners are disclosed in U.S. Pat. No. 6,424,632 assigned to the assignee of the present invention.
To drill a round hole, it is important that the laser spot be relatively stationary with respect to the desired hole location for the duration of the laser pulse. For each hole, the limited rotation motors are rotated to position the mirror at the correct coordinates, and the laser is fired once the limited rotation motors are settled. Generally, the laser pulse is much shorter in duration than the time needed for repositioning the mirrors on the limited rotation motors. For these reasons, the speed of drilling multiple holes is limited by the response rate of the positioning systems, not by laser power. The settling performance of the limited rotation motors is generally limited by the resonant frequency, and the stepping rate (to step and settle) is limited by the efficiency of the motors. Increasing the bandwidth of the motors is, however, constrained by the fact that the power dissipated in limited rotation motors (e.g., in the form of heat) is proportional to the speed to the fifth power.
There remains a need, therefore, for a more efficient and economical laser processing system that improves the efficiency of the positioning system.